Frequency diversity modulation system and method

ABSTRACT

A method of encoding a first bit and a second bit for transmission on a transmission band is provided. The method includes: mapping, via a mapping component, the first bit and the second bit into a first symbol; mapping, via the mapping component, the first bit and the second bit into a second symbol; dividing, via a dividing component, the transmission band into subcarriers; allocating, via an allocating component, the first symbol to a first subcarrier of the subcarriers; allocating, via the allocating component, the second symbol to a second subcarrier of the subcarriers; and differentially encoding, via a differential encoder, the first symbol and the second symbol.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. Nonprovisionalapplication Ser. No. 14/449,981, filed Aug. 1, 2014, which claimspriority from: U.S. Provisional Application No. 61/864,893 filed Aug.12, 2013, the entire disclosures of which are incorporated herein byreference.

BACKGROUND

The present invention is generally drawn to a system and method formodulating transmitted data to improve the robustness of power-linecommunications (PLC).

FIG. 1 illustrates a conventional power-line communications system 100.

As shown in the figure, system 100 includes an AC generator 101, a powertransmission line 102, multiple power transmission line supports 104, atransmitter 110, communication signal transmission lines 112 and 116 anda receiver 114.

AC generator 101 is connected to power transmission line 102, which issupported by power transmission line supports 104. Transmitter 110 isconnected to power transmission line by way of communication signaltransmission line 112. Receiver 114 is connected to power transmissionline 102 by way of communication signal transmission line 116.

AC generator 101 is operable to generate and distribute AC power throughpower transmission line 102 to users not shown. Transmitter 110 isoperable to transmit a communication signal to power transmission line102 through communication signal transmission line 112. Receiver 114 isoperable to receive communication signal transmitted through powertransmission line 102 by way of communications signal transmission line116.

In operation, AC generator 101 generates electrical power to bedistributed to users not shown by way of power transmission line 102,which is supported by multiple power transmission lines supports 104.Transmitter 110 generates a communication signal and transmits thesignal by way of signal transmission line 112 to power transmission line102. The communication signal is propagated by power transmission line102 and delivered to receiver 114 by communication signal transmissionline 116.

Primary impairments that limit communication performance of PLC includefrequency selective channel, narrowband interference, and impulsivenoise. Frequency selective channel impairments refer to signaldistortions that are a function of a frequency within a channel in acommunication line. Frequency selective channel impairments are based onattributes of the communication medium, e.g., the material of the powerline in PLC systems and the different loads on the power-line.Narrowband interference is interference within a small portion of theband transmitted by the transmitter. For example, for purposes ofdiscussion, suppose a transmitter is able to transmit in a band from 0to 500 kHz. In such a transmission scheme, narrowband interference (NBI)may be interference with the band of 50 to 75 kHz. NBI may be due to thepresence of legacy single carrier communication systems on the PLCnetwork, e.g., spread-frequency shift keying (SFSK). Impulsive noise maybe attributed to electrical devices within the power delivery system.All of these impairments may attenuate and/or delay data transmittedover a power line at different amounts based on the transmissionfrequency. These inconsistent attenuations and/or delays may causeerrors in a received signal in PLC system.

Traditionally, repetition coding is used to improve the robustness ofPLC in harsh channel and noise environments, at the price of decreaseddata rates. As an example IEEE P1901.2, ITU-T G.9903 G3-PLC and ITU-TG.9904 PRIME have modes like ROBO (Robust) mode and Super ROBO modewhere the bit is repeated either 4 or 6 times. In this manner, even ifone, or some, of the repeated bits are corrupted during transmission,there is an increased likelihood that one, or many others, of therepeated bits will be correctly received.

Dual carrier modulation (DCM) has been proposed to combat frequencyselective channels in multi-band ultra-wideband (MB-UWB) wirelesscommunication systems using Orthogonal Frequency Division Multiplexing(OFDM) for coherent systems. DCM maps four bits to two different 16-QAMsymbols, which are allocated to two sub-bands that are separated by afixed number of sub-bands. In case one of the two symbols is lost orunrecoverable, it is still possible to recover the four bits from theother symbol. The communication reliability is therefore improved. Using16-QAM however entails that the system is a coherent system and pilotsneed to be sent in order to estimate the channel. In particular, thepilots are used to estimate the amplitude and phase of thefrequency-selective channel. The channel estimation is then used by thereceiver to compensate for amplitude and phase distortion imposed by thechannel to subsequently received data. A disadvantage with coherentsystems is that the introduction of pilots results in a loss of datarate as compared to a differential system.

What is needed is a modulation system and method that addressesimpairments that limit communication performance of PLC and that doesnot decrease data rate as much as conventional systems and methods.

BRIEF SUMMARY

The present invention provides a modulation system and method thataddresses impairments that limit communication performance of PLC andthat does not decrease data rate as much as conventional systems andmethods.

In accordance with aspects of the present invention, a method ofencoding a first bit and a second bit for transmission on a transmissionband is provided. The method includes: mapping, via a mapping component,the first bit and the second bit into a first symbol; mapping, via themapping component, the first bit and the second bit into a secondsymbol; dividing, via a dividing component, the transmission band intosubcarriers; allocating, via an allocating component, the first symbolto a first subcarrier of the subcarriers; allocating, via the allocatingcomponent, the second symbol to a second subcarrier of the subcarriers;and differentially encoding, via a differential encoder, the firstsymbol and the second symbol.

Additional advantages and novel features of the invention are set forthin part in the description which follows, and in part will becomeapparent to those skilled in the art upon examination of the followingor may be learned by practice of the invention. The advantages of theinvention may be realized and attained by means of the instrumentalitiesand combinations particularly pointed out in the appended claims.

BRIEF SUMMARY OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe specification, illustrate an exemplary embodiment of the presentinvention and, together with the description, serve to explain theprinciples of the invention. In the drawings:

FIG. 1 illustrates a conventional power-line communications system;

FIG. 2 illustrates a dual carrier modulation (DCM) scheme, in accordancewith aspects of the present invention;

FIG. 3A illustrates an example of an 8PSK mapping constellation;

FIG. 3B illustrates another example of an 8PSK mapping constellation;

FIG. 4A illustrates an example 16PSK mapping constellation;

FIG. 4B illustrates another example 16PSK mapping constellation;

FIG. 5 illustrates an example of 16APSK mapping constellation;

FIG. 6 illustrates a differential modulation scheme to be applied afterDCM, in accordance with aspects of the present invention;

FIG. 7 illustrates an example of a differential encoding system inaccordance with aspects of the present invention;

FIG. 8 illustrates an example orthogonal frequency division multiplexing(OFDM) transmitter using frequency diversity modulation (FDM), inaccordance with aspects of the present invention; and

FIG. 9 illustrates an exploded view of an example implementation of thedifferential encoder of FIG. 8, in accordance with aspects of thepresent invention.

DETAILED DESCRIPTION

An aspect of the present invention is drawn to differentially modulatinga dual carrier modulation (DCM) for transmission through a PLC toalleviate receiver implementation complexity due to channel estimation.Another aspect of the present invention is drawn to a frequencydiversity modulation for transmission through a PLC to reduce effects oftransmission impairments of the transmission line as a function offrequency.

On a transmitter side of a PLC system, M bits of data to be transmittedare mapped to M symbols, within M sub-carriers. These M symbols may thenbe differentially modulated to create a differentially modulated stringof symbols. This differentially modulated string of symbols may then beused to create an orthogonal frequency division multiplexing (OFDM) wordfor transmission through a power line to a receiver. The receiver, maythen perform inverse transformations to decode the received data toobtain the original M bits of data.

Example embodiments, in accordance with aspects of the presentinvention, will now be described in greater detail with reference toFIGS. 2-9.

An example of a modulation scheme, in accordance with aspects of thepresent invention, will now be described in greater detail withreference to FIGS. 2 and 6.

FIG. 2 illustrates a dual carrier modulation (DCM) scheme, in accordancewith aspects of the present invention.

As shown in figure, the DCM scheme includes a bit stream 202 and astream of symbols 204. Bit stream 202 includes a plurality of binarybits, examples of which are 206, 208, 210 and 212. Stream of symbols 204includes a plurality of symbols, examples of which are 214, 216, 218 and220. Stream of symbols 204 are assigned to sub-bands 222 and 224, eachof which is divided into subcarriers, examples of which are 226, 228,230 and 232.

The DCM scheme maps a group of bits to a symbol, which is assigned a tosub-band, examples of which are: bit 206 and bit 210 being mapped tosymbol 214 as indicated by lines 234 and 236, respectively; bit 206 andbit 210 being mapped to symbol 218 as indicated by lines 238 and 240,respectively; bit 208 and bit 212 being mapped to symbol 216 asindicated by lines 242 and 244, respectively; and bit 208 and bit 212being mapped to symbol 220 as indicated by lines 246 and 248,respectively.

It should be noted that in the example as shown in FIG. 2, only two bitsare mapped to two symbols. However, as will be described later, inaccordance with aspects of the present invention, M bits may be mappedto M symbols, wherein M is a positive integer.

In accordance with aspects of the present invention, the mapping of bitsto symbols as described in FIG. 2 will be discussed in greater detailwith reference to FIGS. 3A-5.

There exist a large number of possible symbol mappings, however, thereare optimal symbol mappings that can be chosen to minimize the symbolerror rate. Bits may be mapped to symbols by any known method,non-limiting examples of which include Phase-shift keying (PSK) andAmplitude and phase-shift keying or asymmetric phase-shift keying(APSK).

Example mappings for mapping three bits to three 8PSK symbols, inaccordance with aspects of the present invention, will now be describedin greater detail with reference to FIGS. 3A-B. This mapping may beoptimal for a particular noise and channel condition.

FIG. 3A illustrates an example of an 8PSK mapping constellation 300.

Phase-shift keying (PSK) is a digital modulation scheme that conveysdata by changing, or modulating, the phase of a reference signal (thecarrier wave). Any digital modulation scheme uses a finite number ofdistinct signals to represent digital data. PSK uses a finite number ofphases, each assigned a unique pattern of binary digits. Usually, eachphase encodes an equal number of bits. Each pattern of bits forms thesymbol that is represented by the particular phase. The demodulator,which is designed specifically for the symbol-set used by the modulator,determines the phase of the received signal and maps it back to thesymbol it represents, thus recovering the original data. This requiresthe receiver to be able to compare the phase of the received signal to areference signal—such a system is termed coherent (and referred to asCPSK). 8PSK is a PSK scheme that maps eight different digital words,i.e., three binary bits, to eight symbols.

As shown in the figure, constellation 300 has an x-axis 302, a y-axis304 and a radius 306. The constellation allows mappings for 8 binarynumbers, for example a bit stream 000 as indicated by 308 lies on radius306 at phase angle 0°, a bit stream 001 as indicated by 310 lies onradius 306 at phase angle 315° and a bit stream 010 as indicated by 312lies on radius 306 at phase angle 45°. The mappings are spaced aroundradius 306 at integer multiples of phase angle 322 which has a value of45°.

A bit stream corresponds to the different bits that are mapped to asingle symbol. For example, consider bit stream 001 as indicated by 310.For purposes of discussion, returning to FIG. 2, let the first bit value“1” in bit stream 001 correspond to bit 206, let the second bit value“0” in bit stream 001 correspond to bit 210, and let the third bit value“0” in bit stream 001 correspond to another bit (not shown), that isseparated from bit 210. In this example, therefore, the symbol inconstellation 300 that corresponds to bit stream 001 corresponds to thebit values of three separated bits in bit stream 202. Accordingly,information corresponding to a unit radius, in this example radius 306,and a specific phase, in this example 315°, sufficiently describes thevalues of three distinct bits in bit stream 202.

Then, consider bit stream 010 as indicated by 312. For purposes ofdiscussion, returning to FIG. 2, let the first bit value “0” in bitstream 001 correspond to bit 208, let the second bit value “1” in bitstream 010 correspond to bit 212, and let the third bit value “0” in bitstream 010 correspond to another bit (not shown), that is separated frombit 212. In this example, therefore, the symbol in constellation 300that corresponds to bit stream 010 corresponds to the bit values ofthree separated bits in bit stream 202. Accordingly, informationcorresponding to a unit radius, in this example radius 306, and aspecific phase, in this example 45°, sufficiently describes the valuesof three distinct bits in bit stream 202.

This mapping continues until all bits within bit stream 202 are mappedto a symbol. In some embodiments, all mappings are performed to a singleconstellation. In some embodiments mappings may be performed todifferent constellations.

FIG. 3B illustrates another example of an 8PSK mapping constellation,314.

As shown in the figure, constellation 314 has an x-axis 301, a y-axis303 and a radius 305. The constellation allows mappings for 8 binarynumbers, spaced around radius 305 at integer multiples of a phase angleof 45°.

Constellation 314 differs from constellation 300 in that values for thebit streams 001 indicated by 310, 010 indicated by 312, 110 indicated by316 and 101 indicated by 318 have been mapped 225°, 135°, 45° and 315°respectively.

Consider now for example, a bit stream corresponds to the different bitsthat are mapped to a single symbol. For example, consider bit stream 001as indicated by 310. For purposes of discussion, returning to FIG. 2,let the first bit value “1” in bit stream 001 correspond to bit 206, letthe second bit value “0” in bit stream 001 correspond to bit 210, andlet the third bit value “0” in bit stream 001 correspond to another bit(not shown), that is separated from bit 210. In this example, therefore,the symbol in constellation 314 that corresponds to bit stream 001corresponds to the bit values of three separated bits in bit stream 202.Accordingly, information corresponding to a unit radius, in this exampleradius 306, and a specific phase, in this example 225°, sufficientlydescribes the values of three distinct bits in bit stream 202.Accordingly, as compared to constellation 300 of FIG. 3A, wherein bitstream 001 corresponded to a symbol associated with a phase of 315°, inconstellation 314 of FIG. 3B, bit stream 001 corresponds to a symbolassociated with a phase of 225°.

Then, consider bit stream 010 as indicated by 312. For purposes ofdiscussion, returning to FIG. 2, let the first bit value “0” in bitstream 001 correspond to bit 208, let the second bit value “1” in bitstream 010 correspond to bit 212, and let the third bit value “0” in bitstream 010 correspond to another bit (not shown), that is separated frombit 212. In this example, therefore, the symbol in constellation 314that corresponds to bit stream 010 corresponds to the bit values ofthree separated bits in bit stream 202. Accordingly, informationcorresponding to a unit radius, in this example radius 306, and aspecific phase, in this example 135°, sufficiently describes the valuesof three distinct bits in bit stream 202. Accordingly, as compared toconstellation 300 of FIG. 3A, wherein bit stream 010 corresponded to asymbol associated with a phase of 45°, in constellation 314 of FIG. 3B,bit stream 010 corresponds to a symbol associated with a phase of 135°.

In the non-limiting examples discussed above, bits may be mapped tosymbols by a single constellation, or by a plurality of constellations.So long as a receiver has knowledge of the encoding scheme used by atransmitter, the receiver will be able to decode non-compromised data byany known manner or system.

The non-limiting example 8PSK mapping discussed above with reference toFIGS. 3A-B enable mapping of three binary bits to a single 8PSK symbol,of an 8-symbol set. However, aspects of the present invention may beapplied to larger symbol sets.

Example mappings for mapping 4 bits to 4 16PSK constellations, inaccordance with aspects of the present invention, will now be describedin greater detail with reference to FIGS. 4A-B.

Example mappings for 16PSK constellations, in accordance with aspects ofthe present invention, will now be described in greater detail withreference to FIGS. 4A-B.

FIG. 4A illustrates an example 16PSK mapping constellation, 400.

As shown in the figure, constellation 400 has an x-axis 402, a y-axis404 and a radius 406. Bit streams map to symbols at radius 406 at aninteger multiple of a phase angle of 22.5°, example bit streams of whichare labeled 408, 410 and 412. With constellation 400, 16 binary numbers,each of which consists of four binary bits, are mapped to 16 symbols,respectively. For example a bit stream 0010 as indicated by 408 lies onradius 406 at a phase angle of 67.5°, a bit stream 0011 as indicated by410 lies on radius 406 at a phase angle of 45° and a bit stream 0001 asindicated by 412 lies on radius 406 at a phase angle of 22.5°.

With a 16PSK mapping constellation, four separated bits may be mapped toa single symbol. The mapping continues until all bits within a bitstream are mapped to a symbol. In some embodiments, all mappings areperformed to a single constellation. In some embodiments mappings may beperformed to different constellations.

FIG. 4B illustrates another example 16PSK mapping constellation, 414.

As shown in the figure, constellation 414 has x-axis 402, y-axis 404 andradius 406. Bit streams map to symbols at radius 406 at an integermultiple of a phase angle of 22.5°, example bit streams of which arelabeled 416, 418 and 620. With constellation 414, 16 binary numbers,each of which consists of four binary bits, are mapped to 16 symbols,respectively. For example a bit stream 0001 as indicated by 416 lies onradius 406 at a phase angle of 67.5°, a bit stream 1001 as indicated by418 lies on radius 406 at a phase angle of 45° and a bit stream 1101 asindicated by 620 lies on radius 406 at a phase angle of 22.5°. As such,by comparing constellation 400 of FIG. 4A with constellation 414 of FIG.4B, a symbol of a radius and a specific angle in constellation 400corresponds to a different bit stream than a symbol of the same radiusand the same specific angle in constellation 414. For example, bitstream 408 of constellation of 400 is different from bit stream 416 ofconstellation 414, even though each will have the same 16PSK symbol.

In the non-limiting examples discussed above, bits may be mapped tosymbols by a single 16PSK constellation, or by a plurality of 16PSKconstellations. So long as a receiver has knowledge of the encodingscheme used by a transmitter, the receiver will be able to decodenon-compromised data by any known manner or system.

The non-limiting example 8PSK and 16PSK mapping discussed above withreference to FIGS. 3A-4B enable mapping of three binary bits to a single8PSK symbol, of an 8-symbol set, and four binary bits to single 16PSKsymbol, of a 16-symbol set, respectively. However, aspects of thepresent invention may be applied to larger symbol sets, by additionallyaddressing changes in amplitude of the symbol.

As mentioned above, as possible that at least one of the constellationscould be an APSK constellation, an example of which will now bediscussed in FIG. 5.

FIG. 5 illustrates an example of 16APSK mapping constellation.

Amplitude and phase-shift keying or asymmetric phase-shift keying(APSK), is a PSK scheme that conveys data by changing, or modulating,both the amplitude and the phase of a reference signal (the carrierwave). In other words, it combines both amplitude-shift keying (ASK)with the phase-shift keying (PSK) to increase the symbol-set.

As shown in the figure, there is an x-axis 500, a y-axis 502, a radius504 and a radius 508. The constellation allows mapping for 16 binarynumbers to 16 symbols, examples of which are indicated by 506 and 510.

Bit streams map to symbols at radius 504 at an integer multiple of aphase angle of 30°, an example symbol of which is labeled 506. Other bitstreams map to symbols at radius 508 at an integer multiple of a phaseangle of 45°, an example symbol of which is labeled 510.

As compared to the 8PSK and 16PSK constellation mapping discussed abovewith reference to FIGS. 3A-4B, an APSK constellation, for example asdiscussed with reference to FIG. 5, enables differentiation betweensymbols additionally based on radius.

The non-limiting example 8PSK, 16PSK and APSK mapping discussed abovewith reference to FIGS. 3A-5 do not limit the scope of the invention,but are merely provided for purposes of discussion. It should be notedthat any known mapping scheme may be used.

Returning to FIG. 2, as illustrated by lines 234 and 236, the DCM schememaps bit 206 and bit 210 of bit stream 202 to a symbol 214, which isassigned to subcarrier 226 within sub-band 222. Further, as illustratedby lines 238 and 240, the DCM maps bit 206 and bit 210 to a symbol 218,which is assigned to subcarrier 230 within sub-band 224. In this exampleDCM scheme, two bits, for example bit 206 and bit 210, are mapped to twosymbols, for example symbol 214 and symbol 218. Each symbol is assigneda different subcarrier, for example subcarrier 226 and subcarrier 230,respectively.

The DCM scheme transmits two symbols, examples of which are 214 and 218,over two subcarriers separated by a number of subcarriers in a way thatthey experience independent channel distortion and noise. As such, ifsymbol 214 were compromised in transmission as a result of channelimpairments that are a function of channel frequency, it is less likelythat symbol 218 will be compromised by similar channel impairments asthe two symbols are transmitted through separated and distinctsubcarriers, 226 and 230, respectively. This provides diversity and isused to improve communication system reliability.

The first aspect of the invention extends DCM to a generalized frequencydiversity modulation (FDM) scheme. The FDM scheme divides thetransmission band into several different sub-bands, for example 222 and224. There could, however, be M sub-bands.

In general, the FDM scheme maps M bits to M symbols. The M symbols arethen allocated to M subcarriers. Each subcarrier is located within oneindividual sub-band. For example two bits, 206 and 210, are each mappedto two different symbols, 214 and 218. Symbol 214 is located in sub-band222 and symbol 218 is located in sub-band 224.

A second aspect of the invention extends the application of differentialmodulation after DCM and will now be discussed with respect to FIG. 6.

FIG. 6 illustrates a differential modulation scheme to be applied afterDCM, in accordance with aspects of the present invention.

The figure shows a symbol stream 602 arranged in a differentiallymodulated scheme as indicated by arrows 604. Symbol stream 602 containsa pilot symbol 606 and differential symbols, examples of which aresymbol 608 and symbol 610.

FIG. 6 shows differential modulation scheme 604 differentially modulatessymbol 214 from subcarrier 226, shown in FIG. 2, with pilot symbol 606resulting in differential symbol 608 contained in subcarrier 226.Subsequent differentially modulated symbols, for example differentialsymbol 610 in subcarrier 230, result as subcarriers in sub-bands 214 and216 are differentially modulated based on the value contained in theprevious subcarrier.

In an example embodiment of the present invention, subcarrier 226containing symbol 214 discussed in FIG. 2, is differentially modulatedwith pilot symbol 606 resulting in differential symbol 608. Subsequentsymbols are differentially modulated based on the value of the previoussubcarrier resulting in symbol stream 602.

Differential modulation may occur in the frequency domain and the timedomain using orthogonal frequency division multiplexing (OFDM) symbolstreams. Each of the OFDM symbol streams contains several subcarriers.The first subcarrier of the OFDM symbol stream contains a pilot symbol.The next subcarrier is differentially modulated based on the value ofthe pilot symbol. Subsequent subcarriers are differentially modulatedbased on the value of the previous subcarrier resulting in the finalOFDM symbol stream.

In an example embodiment of the present invention, subcarrier 218containing symbol 214 discussed in FIG. 2, is differentially modulatedwith pilot symbol 606 resulting in differential symbol 608. Subsequentsymbols are differentially modulated based on the value of the previoussubcarrier resulting in symbol stream 602.

The differential modulation alleviates the receiver from the additionalcomplexity for channel estimation. Since the data is encoded in thephase difference between two symbols, subtracting the phases of the tworeceived symbols will automatically cancel the phase distortion,assuming that the channel remains approximately constant between the twosymbols.

Both aspects of the invention, discussed above in FIGS. 2 and 6, willnow be discussed in example embodiment of the present invention withrespect to FIG. 7.

FIG. 7 illustrates an orthogonal frequency division multiplexing (OFDM)transmitter 700 using frequency diversity modulation (FDM), inaccordance with aspects of the present invention.

As shown in the figure, transmitter 700 includes a bit stream 702, aforward error correcting (FEC) component 704, a bit interleave component708, a mapping component 712, bits, examples of which are 713, 714 and715, symbols, an example of which is 719, a differential encoder 725, apilot symbol 721, differentially encoded sub-bands, examples of whichare 722, 723 and 724, an OFDM symbol stream 726, an inverse fast Fouriertransform (IFFT) component 728, a signal 730, mappings 716, 717 and 718,and communication channels 706, 710 and 720. Communication channels 706,710 and 720 may be any known type of channel for transferring data,non-limiting examples of which include wired and wireless.

FEC component 704 connects to bit interleave component 708 bycommunication channel 706. Bit interleave component 708 is connected tomapping component 712 by communication channel 710. Symbol 719 istransmitted to differential encoder 725 by communication channel 720.

FEC component 704 and bit interleave component 708 are operable toprotect binary information against burst errors prior to FDM. Mappingcomponent 712 is operable to map bit 713, bit 714 and bit 715 to symbol719 by mappings 716, 717 and 718, respectively. The bits are mapped tosubsequent symbols in the same manner. Differential encoder 725 isoperable to encode symbols, for example symbol 719 with pilot symbol721, to produce differentially encoded symbols in sub-bands 722, 723 and724 and generate OFDM symbol stream 726. IFFT component 728 is operableto generate signal 730.

The raw bit stream 702 is preconditioned to protect against burst errorsFEC 704 and bit interleave component 708. Burst errors can result fromcompulsive noise contaminating consecutive bits in the bit stream 702.FEC component 704 performs forward error correction on the input bitstream. The bit interleave component 708 permutes bits throughout thebit stream and reduces error propagation.

In accordance with the first aspect of the present invention, asdiscussed above in FIG. 6, FDM is applied to the bit stream. Bits aremapped into sub-bands, examples of which are 713, 714 and 715, bymapping component 712 and allocated to symbols, an example of which issymbol 719, within each sub-band.

In accordance with the second aspect of the present invention, asdiscussed above in FIG. 6, the sub-bands are differentially modulated inthe frequency domain. Differential encoder 725 differentially modulatesthe first symbol of sub-band 722 with pilot symbol 721. Subsequentsymbols are differentially modulated using the value of the previoussymbol resulting in sub-bands 722, 723 and 724, resulting in OFDM symbolstream 726.

The IFFT component 728 converts OFDM signal 726 from the frequencydomain to the time domain resulting in signal 730.

In operation, bit stream 702 is preconditioned by FEC component 704 andbit interleave component 708 to minimize susceptibility of the data toburst errors. Mapping component 712 maps the individual bits tosub-bands, examples of which are 713, 714 and 715. Each bit is thenmapped to a symbol in each sub-band, an example of which is 719.Differential encoder 725 differentially modulates the symbol streamcontaining the bitmapped symbols. Differential encoder 725 generatespilot symbol 721 and differentially modulates the first symbol ofsub-band 722 with pilot symbol 721. Subsequent symbols from eachsub-band are differentially modulated based on the value of the previoussymbol, generating OFDM symbol stream 726. OFDM symbol stream 726 istransformed from the frequency domain to the time domain by IFFTcomponent 728 resulting in signal 730.

FIG. 8 illustrates an example of a differential encoding system 800, inaccordance with aspects of the present invention.

As shown in the figure, system 800 includes bit 802, bit 804, mappingcomponent 806, mappings 808, 810, 812 and 814, symbol 816, symbol 818,allocating component 828, transmission band 822, dividing component 820,subcarriers 824 and 826, differential encoder 725 of FIG. 7, symbolstream 834 and communication channels 836, 838, 840 and 842.Communication channels 836, 838, 840 and 842 may be any known type ofchannel for transferring data, non-limiting examples of which includewired and wireless.

Mapping component 806 is connected to allocating component 828 bycommunication channel 836 and communication channel 838. Dividingcomponent 820 is connected to allocating component 828 by communicationchannel 840. Allocating component 828 is connected to differentialencoder 725 by communication channel 842.

Mapping component 806 is operable to encode bit 802 to symbol 816 bymapping 808 and to symbol 818 by mapping 814. Mapping component 806 isoperable to encode bit 804 to symbol 816 by mapping 810 and to symbol818 by mapping 812. Mapping component 806 is operable to transmit symbol816 to allocating component 828 by communication channel 836. Mappingcomponent 806 is operable to transmit symbol 818 to allocating component828 by communication channel 838.

Dividing component 820 is operable to divide transmission band 822 intosubcarrier 824 and subcarrier 826. Dividing component 820 is operable totransmit subcarrier 824 and subcarrier 826 to allocating component 828by communication channel 840.

Allocating component 828 is operable to allocate symbol 816 tosubcarrier 824 and symbol 818 to subcarrier 826 and transmit the encodedsubcarriers to differential encoder 725 by communication channel 842.

Differential encoder 725 is operable to differentially encode symbol 816and symbol 818. Differential encoder 725 is operable to produce symbolstream 834.

The first aspect of the present invention, which extends DCM to ageneral FDM scheme as described in FIGS. 2 and 6, will now be discussed.

Mapping component 806 maps bits 802 and 804 to symbol 816 in a firstsub-band by mapping 808 and 814 respectively. Mapping component 806 alsomaps bits 802 and 804 to symbol 818 in a second sub-band by mapping 810and 812 respectively.

Transmission band 822 is divided into two subcarriers 824 and 826 bydividing component 820. Allocating component 828 allocates symbol 816 tosubcarrier 824 in the first sub-band and symbol 818 to subcarrier 826 inthe second sub-band.

The second aspect of the present invention, which extends theapplication of differential modulation after DCM as discussed in FIGS. 2and 6, is accomplished as differential encoder 725 encode the symbolstream containing symbols 816 and 818, resulting in symbol stream 834and is described in greater detail in FIG. 8.

Differential encoder 725 will now be discussed in greater detail.

FIG. 9 illustrates an exploded view of an example implementation ofdifferential encoder 725 as discussed above with reference to FIG. 8, inaccordance with aspects of the present invention.

As shown in FIG. 9, differential encoder 725 includes symbol 816, symbol818, packet generator 900, pilot symbol 902, differential component 904,differential component 908, symbol 906, communication channels 910 and912, and symbol stream 834. Communication channels 910 and 912 may beany known type of channel for transferring data, non-limiting examplesof which include wired and wireless.

Packet generator 900 is connected to differential component 904 bycommunication channel 910. Differential component 904 is connected todifferential component 908 by communication channel 912.

Packet generator 900 is operable to produce pilot symbol 902 andtransmit a signal to differential component 904 by communication channel910. Differential component 904 is operable to differentially encodepilot symbol 902 and symbol 816 to produce symbol 906 and transmitsymbol 906 to differential component 908 by communication channel 912.Differential component 908 is operable to differentially encode symbol818 with symbol 906 to produce symbol stream 834.

Packet generator 900 generates pilot symbol 902. Differential component904 differentially modulates symbol 816 with pilot symbol 902 resultingin symbol 906. Differential component 908 differentially modulatessymbol 818 with symbol 906 resulting in symbol stream 834.

The foregoing description of various preferred embodiments of theinvention have been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteaching. The example embodiments, as described above, were chosen anddescribed in order to best explain the principles of the invention andits practical application to thereby enable others skilled in the art tobest utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of the invention be defined by the claimsappended hereto.

What is claimed is:
 1. A method of encoding a first bit stream includinga plurality of bits for transmission on a transmission band, the methodcomprising: receiving, via a first input of a mapping component, theplurality of bits of the first bit stream, wherein the plurality of bitsincludes a first bit and a second bit; mapping, via the mappingcomponent, the first bit and the second bit received at the first inputinto a first symbol; mapping, via the mapping component, the first bitand the second bit received at the first input into a second symbol;dividing, via a dividing component, the transmission band intosubcarriers; allocating, via an allocating component, the first symbolto a first subcarrier of the sub carriers; allocating, via theallocating component, the second symbol to a second subcarrier of thesubcarriers; and differentially encoding, via a differential encoder,the first symbol and the second symbol.
 2. The method of claim 1,wherein the first symbol and the second symbol are the same in that thefirst symbol includes the first bit, the second bit, and at least oneother bit and the second symbol includes the first bit, the second bit,and the at least one other bit.
 3. The method of claim 2, wherein thefirst symbol is one of a phase-shift keying (PSK) symbol or an amplitudeand phase-shift keying (APSK) symbol.
 4. The method of claim 1, whereinthe first symbol and the second symbol are different in that the firstsymbol includes the first bit, the second bit, and a third bit of thefirst bit stream and the second symbol includes the first bit, thesecond bit, and a fourth bit of the first bit stream that differs fromthe third bit.
 5. The method of claim 4, wherein the first symbol is oneof a phase-shift keying (PSK) symbol or an amplitude and phase-shiftkeying (APSK) symbol.
 6. A system for encoding a first bit streamincluding a plurality of bits for transmission on a transmission band,the system comprising: a mapping component to receive the plurality ofbits of the first bit stream at a first input of the mapping component,wherein the plurality of bits includes a first bit and a second bit, mapthe first bit and the second bit received at the first input into afirst symbol, and map the first bit and the second bit received at thefirst input into a second symbol; a dividing component to divide thetransmission band into subcarriers; an allocating component to allocatethe first symbol to a first subcarrier of the subcarriers and toallocate the second symbol to a second subcarrier of the subcarriers;and a differential encoder to differentially encode the first symbol andthe second symbol.
 7. The system of claim 6, wherein the first symboland the second symbol are the same in that the first symbol includes thefirst bit, the second bit, and at least one other bit and the secondsymbol includes the first bit, the second bit, and the at least oneother bit.
 8. The system of claim 7, wherein the first symbol is one ofa phase-shift keying (PSK) symbol or an amplitude and phase-shift keying(APSK) symbol.
 9. The method of claim 1, wherein: the transmission bandincludes a plurality of sub-bands including a first sub-band and asecond sub-band; the first sub-band includes a first plurality of thesubcarriers that includes the first subcarrier; the second sub-bandincludes a second plurality of the subcarriers that includes the secondsubcarrier, wherein none of the subcarriers of the second plurality ofthe subcarriers overlaps with any of the subcarriers the first pluralityof the subcarriers; the first symbol allocated to the first subcarrieris assigned to the first sub-band; and the second symbol allocated tothe second subcarrier is assigned to the second sub-band.
 10. The methodof claim 9, wherein: no bit mapped to the first symbol is sequential inthe first bit stream with respect to any other bit mapped to the firstsymbol; and no bit mapped to the second symbol is sequential in thefirst bit stream with respect to any other bit mapped to the secondsymbol.
 11. The method of claim 1, wherein the first sub-carrier and thesecond sub-carrier are separated on the transmission band by at leastone other subcarrier so that the first and second symbols are notdirectly adjacent to each other in the transmission band.
 12. The methodof claim 11, wherein the at least one other subcarrier comprises aplurality of subcarriers.
 13. The method of claim 11, whereindifferentially encoding, via the differential encoder, the first andsecond symbols comprises: generating a pilot symbol using a packetgenerator; generating a first differential symbol based on a differencebetween the pilot symbol and the first symbol using at least onedifferential component, the first differential symbol being contained inthe first subcarrier; for each subcarrier separating the firstsubcarrier and the second subcarrier, generating a respectivedifferential symbol based on a difference between a symbol allocated tothe subcarrier and a differential symbol contained in an immediatelypreceding subcarrier using the at least one differential component, therespective differential symbol being contained in the subcarrier; andgenerating a second differential symbol based on a difference betweenthe second symbol and a differential symbol contained in a subcarrierimmediately preceding the second subcarrier, the second differentialsymbol being contained in the second subcarrier; wherein the subcarrierimmediately preceding the second subcarrier is one of the subcarriersseparating the first subcarrier and the second subcarrier, and whereindifferentially encoding the first and second symbols produces a symbolstream containing the pilot symbol, the first differential symbol, andthe second differential symbol.
 14. The method of claim 13, wherein: thetransmission band includes a plurality of sub-bands including a firstsub-band and a second sub-band; the first subcarrier containing thefirst differential symbol is in the first sub-band; and the secondsubcarrier containing the second differential symbol is in the secondsub-band.
 15. The system of claim 6, wherein: the transmission bandincludes a plurality of sub-bands; a first sub-band of the plurality ofsub-bands includes a first plurality of the subcarriers that includesthe first subcarrier; a second sub-band of the plurality of sub-bandsincludes a second plurality of the subcarriers that includes the secondsubcarrier; wherein none of the subcarriers of the first sub- andoverlaps with any of the subcarriers of the second sub-band; the firstsymbol allocated to the first subcarrier is assigned to the firstsub-band; and the second symbol allocated to the second subcarrier isassigned to the second sub-band.
 16. The system of claim 15, wherein,due to being in different sub-bands, the first subcarrier and the secondsubcarrier have different channel distortion and noise responses. 17.The system of claim 6, wherein the first subcarrier and the secondsubcarrier not adjacent to each other in the transmission band.
 18. Thesystem of claim 17, wherein the first subcarrier and the secondsubcarrier are separated by two or more other subcarriers of thetransmission band.
 19. The system of claim 18, wherein the differentialencoder comprises: a packet generator to generate a pilot symbol; anddifferential components to: generate a first differential symbol basedon a difference between the pilot symbol and the first symbol, whereinthe first differential symbol is contained in the first subcarrier; foreach of the two or more other subcarriers separating the firstsubcarrier and the second subcarrier, generate a respective differentialsymbol based on a difference between a symbol allocated to thesubcarrier and a differential symbol contained in an immediatelypreceding subcarrier, wherein the respective differential symbol iscontained in the subcarrier; generate a second differential symbol basedon a difference between the second symbol and a differential symbolcontained in a subcarrier immediately preceding the second subcarrier,the second differential symbol being contained in the second subcarrierand the subcarrier immediately preceding the second subcarrier being oneof the two or more subcarriers separating the first subcarrier and thesecond subcarrier; and produce a symbol stream containing the pilotsymbol, the first differential symbol, and the second differentialsymbol.